In a mobile communication system having both E-UTRAN (Evolved-Universal Terrestrial Radio Access Network) and UTRAN (Universal Terrestrial Radio Access Network) providing CSFB (CS Fallback), if a large number of mobile stations UE send “RRC Connection Request (RRC connection request signal)” for sending “Extended Service Request (call request signal)” for performing CSFB on particular events such as when an earthquake occurs or a new year, a problem arises in which radio resource congestion leads to disconnection of services.
To solve such a problem, taking the following first and second countermeasures is under consideration in the 3GPP.
In the first countermeasure, a radio base station eNB sends broadcast information including the restriction rate for CSFB in a cell under call restriction. Then, a mobile station UE compliant with LTE (Long Term Evolution) Release supporting the barring scheme for CSFB or later can judges whether or not to perform CSFB call processing based on such restriction information. The first countermeasure thus makes it possible to execute CSFB call restriction on the mobile station UE compliant with LTE Release supporting the barring scheme for CSFB or later.
Here, “supporting the barring scheme for CSFB” indicates having ability to load the restriction information (restriction rate) for CSFB and to make a judgment on restriction based on this restriction information (restriction rate) for CSFB.
The second countermeasure uses a procedure shown in FIG. 9 to enable call restriction on both a mobile station UE compliant with LTE Release not supporting the barring scheme for CSFB and a mobile station UE compliant with LTE Release supporting the barring scheme for CSFB or later.
Specifically, in the procedure shown in FIG. 9, upon receiving “Extended Service Request” regarding CSFB from a mobile station UE during call restriction in Step S4001, an switch MME (Mobility Management Entity) sends the mobile station UE “Service Reject” including “Cause#39” and a timer value in Step S4002.
Upon receiving “Service Reject” in Step S4003, the mobile station UE activates a timer (T3442) and cannot perform call processing until a period specified by the timer value included in “Service Reject” is over.